1. Field of the Invention
This invention relates to a method of taking an X-ray photograph, and an X-ray photographic cassette for use in the method. More particularly, this invention relates to a method of simultaneously recording an X-ray transmission image (hereinafter referred to as a roentgen image) of an object both on an X-ray photographic film and on a stimulable phosphor sheet, and an X-ray photographic cassette for use in the method.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to such radiation as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays or ultraviolet rays, they store a part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to a stimulating ray such as a visible ray, light is emitted from the phosphor in the pattern of the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, and 4,315,318, it has been proposed to use a stimulable phosphor for recording a radiation image of the human body for medical diagnosis. Specifically, the stimulable phosphor is first exposed to a radiation to have a radiation image stored therein, and is then scanned with a stimulating ray which causes it to emit light in the pattern of the stored image. The light emitted from the stimulable phosphor upon stimulation thereof is photoelectrically detected and converted to an electric image signal, which is processed as desired to reproduce a roentgen image of a quality suitable for viewing and diagnostic purposes.
The radiation image system described above can provide information useful for various diagnoses, which can not be obtained by conventional radiography using a silver halide photographic material, and can greatly improve diagnostic accuracy and efficiency.
However, the roentgen image obtained by the above-described special processing sometimes appears very differently from that recorded on the conventional X-ray film through an intensifying screen. Therefore, it is sometimes difficult for a radiotherapist not so experienced in diagnosis with the specially processed roentgen image to fully utilize the useful information contained in the roentgen image. Accordingly, in the radiation image system using a stimulable phosphor, it is convenient for achieving high diagnostic accuracy and efficiency to create several photographs carrying images obtained from the same original radiation image by image processings of different types or degrees and to make a diagnosis upon comparing these photographs. In this case, if the X-ray photograph taken by the conventional method using a silver halide photographic material is also used for diagnosis together with the several photographs mentioned above, even a radiotherapist experienced only in diagnosis with the conventional X-ray photographs can easily diagnose a case with high accuracy and efficiency.
In order to obtain the conventional X-ray photograph in addition to the photographs taken by the radiation image system using a stimulable phosphor, it is necessary to take the former by the conventional radiography and take the latter by the system using a stimulable phosphor. Thus, at least two photographing operations must be carried out and, as a result, the patient must be exposed at least twice to X-rays, i.e. be given at least a double dose. Further, it is difficult to completely match the conditions of the object in two photographing operations. Therefore, when photographing is conducted twice, deviations occur between the two radiation images obtained due to differences in respiration, position and angle of the object, adversely affecting diagnosis and sometimes necessitating further photographing operations.
Accordingly, it is desired to simultaneously record a radiation image both on a stimulable phosphor and on an ordinary X-ray film. One way for achieving this is to stack a cassette containing a stimulable phosphor sheet and a conventional X-ray film cassette one upon the other, and expose the stack of two cassettes to X-rays through an object to simultaneously record a roentgen image thereon. This method is effective to record a roentgen image on two recording media by one exposure to X-rays. In this method, however, the X-ray film and the stimulable phosphor sheet are considerably spaced apart from each other because the cassette case walls and an intensifying screen of the X-ray film cassette intervene therebetween. As a result, X-ray scattering occurs in the space between the X-ray film and the stimulable phosphor, adversely affecting sharpness and resolution of the roentgen image obtained. Further, the intensity of X-rays drops as the energy thereof is absorbed by the recording medium positioned nearer to the X-ray source, so that the recording medium positioned farther from the X-ray source cannot receive sufficient image information.